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Free-Radical Reactions of a Propellane, 2,4-Methano-2,4-didehydroadamantane
Mlinaric-Majerski, Kata,Majerski, Zdenko,Rakvin, Boris,Veksli, Zorica
, p. 545 - 548 (2007/10/02)
2,4-Methano-2,4-didehydroadamantane (1), a prototype small propellane, readily added disulfides and carbon tetrachloride across the central bond to give the corresponding 2,4-disubstituted 2,4-methanoadamantanes.Methyl phenyl disulfide as well as mixtures of dimethyl disulfide and diphenyl disulfide produced 2-(methylthio)-4-(phenylthio)-2,4-methanoadamantane (4) in addition to the symmetrical disulfides, 2,4-bis(methylthio)-2,4-methanoadamantane (2) and 2,4-bis(phenylthio)-2,4-methanoadamantane (3).The simultaneous formation of 2,3, and 4 provides strong evidence that these reactions are indeed free-radical chain processes.Carbon tetrachloride, when present in an excess over 1, generated a strong ESR signal corresponding to the 4-substituted 2,4-methano-2-adamantyl radical (5).The structure of this radical was confirmed by ESR of the radical derived from 2,4-methano-2,4-didehydroadamantane-11,11-d2 (1a), The ESR signal appeared only when carbon tetrachloride was present in an excess over 1, which indicated that 1 was a very efficient free-radical trap.Propellane 1 spontaneously reacted with α-phenyl-N-tert-butylnitrone, a spin-trapping agent, and p-benzoquinone, an electron-deficient olefin.The former reaction led to the corresponding nitroxide radical, and the latter one gave 4-methyleneadamantane-2-spiro-7'-bicyclohept-3'-ene-2',5'-dione (9), most probably via a diradical intermediate.The behavior of 1 in all these reactions is consistent with the partial diradical character of this small propellane and suggests the term "diradicaloid" for such species.
